U.S. patent application number 11/039102 was filed with the patent office on 2005-12-08 for tungsten-iron projectile.
This patent application is currently assigned to Continuous Metal Technology Inc.. Invention is credited to Smith, Timothy G..
Application Number | 20050268809 11/039102 |
Document ID | / |
Family ID | 35446271 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050268809 |
Kind Code |
A1 |
Smith, Timothy G. |
December 8, 2005 |
Tungsten-iron projectile
Abstract
A projectile, including a compacted and sintered mixture of a
plurality of tungsten particles and a plurality of iron particles.
At least a portion of the plurality of iron particles are bonded
together, and no intermetallic compounds or alloys of the tungsten
particles and iron particles are formed during the compaction and
sintering processes. The final density of the projectile is from
about 8.1 grams per cubic centimeter to about 12.1 grams per cubic
centimeter, and no substantial densification occurs during
sintering. A method of producing such a projectile is also
disclosed.
Inventors: |
Smith, Timothy G.; (St.
Marys, PA) |
Correspondence
Address: |
THE WEBB LAW FIRM, P.C.
700 KOPPERS BUILDING
436 SEVENTH AVENUE
PITTSBURGH
PA
15219
US
|
Assignee: |
Continuous Metal Technology
Inc.
Ridgway
PA
|
Family ID: |
35446271 |
Appl. No.: |
11/039102 |
Filed: |
January 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60576325 |
Jun 2, 2004 |
|
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Current U.S.
Class: |
102/517 |
Current CPC
Class: |
F42B 12/72 20130101;
F42B 7/046 20130101; F42B 7/10 20130101 |
Class at
Publication: |
102/517 |
International
Class: |
F42B 010/00 |
Claims
The invention claimed is:
1. A projectile, comprising: a compacted and sintered mixture of a
plurality of tungsten particles and a plurality of iron particles,
wherein at least a portion of the plurality of iron particles are
bonded together; wherein there are no intermetallic compounds or
alloys of the tungsten particles and the iron particles formed;
wherein the final density of the projectile is from about 8.1 grams
per cubic centimeter to about 12.1 grams per cubic centimeter; and
wherein there is no substantial densification occurring as a result
of sintering.
2. The projectile of claim 1, wherein the tungsten particles are in
the form of a tungsten powder.
3. The projectile of claim 1, wherein the tungsten particles are
from about 8 microns to about 30 microns in diameter.
4. The projectile of claim 1, wherein the iron particles are from
about 40 microns to about 200 microns in size.
5. The projectile of claim 1, wherein the iron particles are in the
form of an iron powder.
6. The projectile of claim 1, wherein the iron particles are at
least one of water-atomized iron particles, sponge iron particles
and iron powder.
7. The projectile of claim 1, wherein the tungsten particles and
iron particles are mechanically compacted in a die.
8. The projectile of claim 7, wherein the tungsten particles and
the iron particles are pre-blended prior to compaction.
9. The projectile of claim 1, further comprising a material
additive.
10. The projectile of claim 9, wherein the material additive is at
least one of chemical compound, a polymeric compound, a binder and
a lubricant.
11. The projectile of claim 9, wherein the chemical additive is a
lubricant, wherein the lubricant is added to a mixture of the
tungsten particles and the iron particles, and wherein the
lubricant comprises up to 1% by weight of the mixture.
12. The projectile of claim 9, wherein the material additive is at
least one of ethylenebissterimide, Acrawax C, lithium carbonate, a
carbonate compound, a stearate compound, copper stearate and zinc
stearate.
13. The projectile of claim 1, wherein the mixture is sintered in a
sintering furnace under controllable atmospheric conditions.
14. The projectile of claim 13, wherein the atmospheric conditions
include the use of at least one of a mildly oxidizing gaseous
material, an inert gaseous material and a reducing gaseous
material.
15. The projectile of claim 1, wherein the projectile is sintered
in a solid state sintering process.
16. The projectile of claim 1, wherein the final hardness of the
formed and sintered projectile is from about 10 HB to about 50
HB.
17. The projectile of claim 1, wherein the ratio of the mixture of
tungsten particles to iron particles is, by weight, from about
30:70 to about 65:35.
18. The projectile of claim 1, wherein the projectile is a shot
pellet.
19. The projectile of claim 1, wherein the projectile is a
bullet.
20. The projectile of claim 1, wherein the temperature of the
sintering process is from about 1500.degree. F. to about
2450.degree. F.
21. The projectile of claim 1, wherein the final hardness of the
formed and sintered projectile is less than the final hardness of
steel shot.
22. A method of producing a projectile, comprising the steps of:
mixing a plurality of tungsten particles and a plurality of iron
particles; compacting the mixture, thereby forming the projectile;
and sintering the formed projectile at a temperature sufficient to
form bonds between at least a portion of the plurality of iron
particles, wherein no intermetallic materials or alloys of the
tungsten particles and the iron particles are formed during the
compacting and sintering steps; wherein the final density of the
projectile is from about 8.1 grams per cubic centimeter to about
12.1 grams per cubic centimeter; and wherein no substantial
densification occurs in the sintering step.
23. The method of claim 22, wherein the tungsten particles are in
the form of a tungsten powder.
24. The method of claim 22, wherein the tungsten particles are from
about 8 microns to about 30 microns in diameter.
25. The method of claim 22, wherein the iron particles are from
about 40 microns to about 200 microns in size.
26. The method of claim 22, wherein the iron particles are in the
form of an iron powder.
27. The method of claim 22, wherein the iron particles are at least
one of water-atomized iron particles, sponge iron particles and
iron powder.
28. The method of claim 22, wherein compaction process includes the
step of mechanically compacting of a portion of tungsten particles
and iron particles in a die.
29. The method of claim 28, wherein, prior to compacting the
portion of tungsten particles and the iron particles, the method
further includes the step of blending the tungsten particles and
the iron particles.
30. The method of claim 22, further comprising the step of adding a
material additive to the mixture of tungsten particles and iron
particles.
31. The method of claim 30, wherein the material additive is at
least one of a chemical compound, a polymeric compound, a binder
and a lubricant.
32. The method of claim 30, wherein the chemical additive is a
lubricant, the method further comprising the step of adding the
lubricant to the mixture of the tungsten particles and the iron
particles, wherein the lubricant comprises up to 1% by weight of
the mixture.
33. The method of claim 30, wherein the material additive is at
least one of ethylenebissterimide, Acrawax C, lithium carbonate, a
carbonate compound, a stearate compound, copper stearate and zinc
stearate.
34. The method of claim 22, wherein the formed projectile is
sintered in a sintering furnace under controllable atmospheric
conditions.
35. The method of claim 34, wherein the atmospheric conditions
include the use of at least one of a mildly oxidizing gaseous
material, an inert gaseous material and a reducing gaseous
material.
36. The method of claim 22, wherein the sintering step is a solid
state sintering process.
37. The method of claim 22, wherein the final hardness of the
formed and sintered projectile is from about 10 HRB to about 80
HRB.
38. The method of claim 22, wherein the ratio of the mixture of
tungsten particles to iron particles is, by weight, from about
30:70 to about 65:35.
39. The method of claim 22, wherein the formed and sintered
projectile is a shot pellet.
40. The method of claim 22, wherein the formed and sintered
projectile is a bullet.
41. The method of claim 22, wherein the temperature in the
sintering step is from about 1500.degree. F. to about 2450.degree.
F.
42. The projectile of claim 22, wherein the final hardness of the
formed and sintered projectile is less than the final hardness of
steel shot.
43. A projectile made in accordance with the method of claim 22.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Patent
Application Ser. No. 60/576,325, filed Jun. 2, 2004, which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to the manufacture
of projectiles, such as shot, bullets, pellets and the like, and in
particular to a tungsten and iron-based projectile having unique
density and softness characteristics, and which can be used in the
manufacture of bullets and shot, such as shotgun shot or
pellets.
[0004] 2. Description of Related Art
[0005] Presently, projectiles, such as bullets, shot and pellets,
are manufactured from a variety of materials, including many
metals, such as lead. However, as the use of lead has decreased,
due to well-documented environmental impacts, projectile
manufacturers have turned to other metals to replace these
lead-based projectiles, such as steel. In particular, various
projectiles have been provided, according to the prior art, that
are composed of some mixtures of tungsten, nickel, iron, etc. Using
these metals, the manufacturer can offer a lead-free and
environmentally-safe projectile.
[0006] While these prior art lead-free projectiles are useful in
many applications, they often have density ranges that are outside
the acceptable range for a projectile that effectively emulates a
lead bullet or lead shot. Within the small group that yields
acceptable density there are no offerings in the current art that
are adequately soft and ductile to be used in firearms without
special considerations being made. To be more precise, there are no
offerings that are adequately soft and ductile to be shotgun-choke
responsive. Projectiles made by many of the current manufacturing
routes are often much harder than lead and therefore cannot emulate
the internal ballistic, external ballistic, and terminal ballistic
characteristics of lead-base projectiles and shot.
[0007] As one substitute for lead shot pellets, and according to
the prior art, steel shot pellets have been developed and are in
widespread use. Steel shot falls far short of the density of lead
(7.86 g/cc vs. 11.34 g/cc) and therefore has significantly lower
performance. Further, these steel shot pellets are significantly
harder than lead and therefore are not appropriately deformable and
do not typically produce uniform pattern densities, particularly at
extended range. Further, special considerations need to be made
with regard to the firearm in order for steel shot to be used
safely. In order to provide an effective pattern density, shells
with variably sized pellets have been produced in order to provide
the appropriate pattern density. However, variably sized shot
pellets have varying external and terminal ballistics. Accordingly,
steel shot pellets are not an effective substitute for lead shot.
In all cases with steel shot, performance is significantly limited
by the hardness and density of steel.
[0008] As is known in the art, in the manufacturing of shot,
various powdered metal materials are often compacted and
subsequently sintered in order to form the projectile. This prior
art can be generally subdivided into several distinct
categories:
[0009] One category is considered to be frangible, such that the
projectiles disintegrate upon impact of the target or backstop and
are used mainly for training purposes for law enforcement and
military personnel. The disintegration of these projectiles reduces
the risk of ricochet and therefore is considered to be a safer
choice than other alternatives especially in close range combat
simulation. These materials (by design) are brittle and the
particles must only be lightly bonded in order to meet the
requirements of the application. Some of these materials are
relatively porous, however they lack sufficient bonding to impart
significant ductility to the resulting projectile. Frangible
ammunition utilizing sintering techniques is generally made by one
of two methods: (1) low-temperature solid state sintering, in which
the temperature remains below the solidus temperature of any of the
materials in the mixture; or (2) transient liquid phase sintering,
which is a process where bonding occurs as the temperature is
elevated above the eutectic temperature of two materials and a
temporary liquid is formed. As soon as the liquid forms, it alloys
with the other metal and the melting point rises such that there is
no longer liquid. The result is light metal-to-metal bonding that
relies on the small, weak, and brittle intermetallic compounds that
form at the contact points of the particles as a result of passing
through the eutectic temperature. Several sintered (non polymer
bonded) variants on these basic methods exist, however the goal
remains the same--brittle bonding to achieve the goal of
frangibility.
[0010] A second major category of powdered metal approaches to
ammunition involves mechanical pressing that serves primarily as a
shaping function and sinter-densification to reach the desired
density. This second category of approaches utilizes very fine
metal particles (some of which may be tungsten and iron) that are
sintered at high temperatures (in excess of about 80% of the
melting point) or liquid phase sintered in which the sintering
temperature is at least above the solidus one of the materials.
[0011] In order to densify to near full theoretical density,
powders below about 6 microns are generally used. Such methods are
commonly employed in the manufacture of tungsten heavy alloy
components for a wide range of applications and these methods are
well known in the art. This second category of approaches is
essentially an adaptation of the technology for production of
tungsten heavy alloys for the manufacture of high-density
ammunition components and to a large degree employs the same basic
techniques and principles, which are well published. Densities
greater than lead are possible, with near full theoretical density
commonplace, however these methods produce components with high
hardness values that are very similar to or higher than steel.
[0012] As is taught by the literature with respect to tungsten
heavy alloy production, powdered metals for these approaches are
typically very small and spherical or semi-spherical. The small
size lowers the necessary sintering temperature and allows near
complete densification, however when powder pressing methods are
used, higher levels of polymer are added to compensate for the lack
of mechanical interlocking typical for spherical powders. In
particular, small semi-spherical powders are not readily compacted
in traditional powder metallurgy methods due to a lack of
mechanical interlocking during pressing and require relatively
large amounts of wax or polymer to adhere the particles. The main
reason for this difficulty is that mechanical powder compaction
relies largely on deformation and interlocking of large, irregular
shaped particles to provide the strength required for ejection from
the die. In the case of small semi-spherical powders, the polymer
is used as a "binder", whereas with large irregular powders, it is
used at a much lower level as a "lubricant" to assist in ejection
and does not impart significant strength to the compacted part.
[0013] Typical sintering temperatures for alloys containing
tungsten and iron are above 1450.degree. C. and require the use of
special high-temperature furnaces. Lower temperatures can be used,
however sintered density is greatly reduced, thus becoming
self-defeating. Further, such high-temperature or liquid phase
sintering of tungsten alloys requires the use of high levels of
hydrogen in the sintering atmosphere in order to reduce the surface
oxides present on the powder surfaces. Because the surface area for
a given mass increases as particle size decreases and surface
oxides are always present at some level, there is a larger
proportion of metal oxide present with smaller particles. This
oxide must be reduced prior to pore closure during sintering or
gasses that evolve from the reduction of these oxides will create
trapped porosity. This phenomenon is well documented in the
literature and is sometimes termed hydrogen embrittlement due to
the fact that oxides trapped in the interstitial spaces between
particles can form water molecules in the presence of hydrogen.
These trapped water molecules are too large to escape through the
matrix or grain boundaries and therefore increase the brittleness
of the material due to pores remaining after sintering. Further,
due to the high binder content necessitated by the particle shape,
surface oxides are not acted upon by mechanical smearing as much as
with larger irregular powders due to the lubricating hydraulic
boundary layer effect that the excess binder produces.
[0014] In systems with a high and low melting point material, such
as tungsten and iron containing systems using high temperature or
liquid state sintering processes, significant bonding occurs
between the high melting point metals due to the enhanced mobility
of the atoms of the high melting point metal within the liquid
matrix. However, depending upon several factors, such as solubility
limit, the amount of higher melting point metal, processing
temperatures, etc., a solid solution may result after cooling,
which can have a wide range of microstructural characteristics from
fine dispersed grains to very large solid interconnected grains. In
the case of a two-metal system in which there is no solubility of
the higher melting point metal in the matrix, no solid solution
will occur, and sintering relies instead on liquid filling in the
spaces between the higher melting point particles. In liquid phase
sintering, the liquid that is formed greatly increases the surface
contact area between particles and dramatically increases mass
transport mechanisms. This subsequently leads to rapid rounding of
porosity and densification. The use of smaller particles is
beneficial in this type of processing due to the inverse
relationship between particle size (diameter) and surface energy,
as is well described in the literature. As particle size is
decreased, the ratio of surface area to volume is increased, thus
creating an energy gradient promoting mass transfer between
particles. See FIG. 6. This driving force slows as surface area
(and consequently surface energy) is reduced until equilibrium
conditions are approached and densification essentially ceases.
[0015] Another factor that provides drawbacks to prior art
projectiles and shot arises from the sintering temperatures and
resulting structures of the mixed compound. For example, many of
the mixtures of metals are sintered at a temperature where an
alloy, intermetallic, metal matrix, etc. are formed. The need for
these higher temperatures and highly reducing atmospheres
significantly increase the processing costs associated with this
sintering method. The formation of these materials and compounds
has particular drawbacks to the resulting softness (or hardness) of
the projectile. This type of system, where mass transport is great,
can result in the widespread formation of intermetallic compounds
in tungsten-iron systems, as tungsten atoms are highly mobile in
iron at this temperature range. Higher levels of intermetallic
compounds lead to decreasing ductility. In addition to the reduced
hardness of the present invention, the larger amount of retained
porosity allows for the projectile to be easily deformed by a
shotgun choke. This, in turn, improves ballistic performance.
SUMMARY OF THE INVENTION
[0016] It is, therefore, an object of the present invention to
provide a tungsten-iron projectile and method of manufacturing the
same that overcomes the deficiencies of the prior art, such as high
hardness, brittleness, high manufacturing cost, etc. It is another
object of the present invention to provide a tungsten-iron
projectile and method of manufacturing the same that includes and
results in a projectile having the appropriate emulation
characteristics with respect to lead-based materials and similar
functionalities. It is yet another object of the present invention
to provide a tungsten-iron projectile and method of manufacturing
the same, where the projectile is significantly softer than
currently-produced sintered, powder based, non-frangible
projectiles. It is a still further object of the present invention
to provide a tungsten-iron projectile and method of manufacturing
the same, which includes and results in a projectile having a
variable density in a specific and desired range. It is another
object of the present invention to provide a tungsten-iron
projectile and method of manufacturing the same, where the
projectile has significantly reduced hardness over currently
produced tungsten-iron-containing shot. It is a still further
object of the present invention to provide a tungsten-iron
projectile and method of manufacturing the same that is
particularly useful as shot for, for example, shotguns. It is yet
another object of the present invention to provide a tungsten-iron
projectile and method of manufacturing the same, where the
projectile is not frangible and possesses significant ductility
without brittle failure.
[0017] Accordingly, the present invention is directed to a
projectile. Specifically, the projectile includes a compacted and
sintered mixture of tungsten particles and iron particles. At least
a portion of the iron particles are bonded together. During the
compacting and sintering processes, there are no intermetallic
compounds, alloys or metal matrices formed between the tungsten
particles and iron particles. In addition, the final density of the
projectile is from about 8.1 grams per cubic centimeter to about
12.1 grams per cubic centimeter. Further, there is no substantial
densification occurring during the sintering process.
[0018] In one embodiment, the tungsten particles are from about 8
microns to about 30 microns in diameter. The iron particles are
from about 40 microns to about 200 microns in size and are
non-spherical. In addition, both the tungsten particles and the
iron particles may be shaped such that they can be used in a cold
compaction powdered metallurgy process.
[0019] In another embodiment, the mixture is sintered in a
sintering furnace under controlled atmospheric conditions, such as
the use of a mildly oxidizing gaseous material, an inert gaseous
material, a reducing gaseous material, etc. Further, the projectile
is sintered in a solid state sintering process where no applicable
densification occurs (i.e., reduction in porosity) and is formed
with a final hardness from about 10 HRB to about 80 HRB. The ratio
of the mixture of tungsten particles to iron particles is, by
weight, from about 30:70 to about 65:35.
[0020] The present invention is also directed to a method of
producing a projectile. This method includes the steps of: (a)
mixing a plurality of tungsten particles and a plurality of iron
particles; (b) compacting the mixture, thereby forming the
projectile; and (c) sintering the formed projectile at a
temperature sufficient to form bonds between a portion of the
plurality of iron particles. During the compacting and sintering
processes and steps, there are no intermetallic materials, alloys
or metal matrices formed between the tungsten particles and iron
particles and there is no substantial densification. Furthermore,
the final density of the projectile is from about 8.1 grams per
cubic centimeter to about 12.1 grams per cubic centimeter.
[0021] The present invention, both as to its construction and its
method of operation, together with the additional objects and
advantages thereof, will best be understood from the following
description of exemplary embodiments when read in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a photograph of a compacted and sintered
projectile according to the present invention;
[0023] FIG. 2 is a photomicrograph of one embodiment of the
projectile according to the present invention magnified at 200
times;
[0024] FIG. 3 is a photomicrograph of one embodiment of the
projectile according to the present invention magnified at 400
times;
[0025] FIG. 4 is an equilibrium phase diagram for tungsten and iron
illustrating the operating region of the manufacturing method
according to the present invention;
[0026] FIG. 5 is a graph plotting density versus tungsten content
at various theoretical densities in manufacturing the projectile
according to the present invention; and
[0027] FIG. 6 is a graph plotting surface area of tungsten as a
function of particle diameter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Other than in the operating examples or where otherwise
indicated, all numbers or expressions referring to quantities of
ingredients, reaction conditions, etc., used in the specification
and claims are to be understood as modified in all instances by the
term "about." Various numerical ranges are disclosed in this patent
application. Because these ranges are continuous, they include
every value between the minimum and maximum values. Unless
expressly indicated otherwise, the various numerical ranges
specified in this application are approximations.
[0029] For purposes of the following discussion, a single melting
point material is a material whose solidus and liquidus is the same
temperature. An example of a single melting point material is a
pure metallic element. In particular, the melting point of iron is
2800.degree. F. (1538.degree. C.), and the melting point of
tungsten is 6191.degree. F. (3422.degree. C.). The solidus of a
material is a temperature for which the material first liquifies.
In particular, below this temperature, the material is a solid and
no liquid is present. Between the solidus and liquidus states,
there is a slushy state, which becomes more liquid as it approaches
the liquidus. This slushy state is observed in the melting of many
alloys. According to the prior art, it is in this temperature range
above the solidus that liquid phase sintering occurs. Liquid phase
sintering can be further broken down into many sub-groups such as
supersolidus sintering and true liquid phase sintering, however all
subcategories of liquid phase sintering occur above the solidus
temperature.
[0030] The liquidus is the temperature for a material at which
there is complete liquid, without any solids present. Above this
temperature, melt processing occurs, such as casting. A system may
be considered a two-material system with high and low melting
constituents, in which the low melting point metal has its own
single melting point or solidus-liquidus range, and yet another
solidus-liquidus range for a solution of the two metals. Many prior
art processes employ melt processing of tungsten-based alloys.
[0031] A solid solution is generally considered a material with
solid particles that have dissolved in a lower melting point matrix
metal. The matrix dissolves the solid particles, which go into
solution. Depending upon several factors, such as the amount of
each metal, dwell-time at the temperature, oxide level present,
processing temperature, cooling rate, etc., the solid particles may
remain very small or may precipitate and grow into larger grains.
In a powdered metal system containing only tungsten and iron,
tungsten atoms have a low probability of becoming mobile until very
high temperatures are reached. Mobility is further slowed by
increases in particle size due to reduced surface energy.
[0032] Liquid phase sintering, as discussed above in detail, is a
sintering process that occurs at a temperature above the solidus of
one or more of the constituent materials. Solid state sintering is
a sintering process that occurs at a temperature below the solidus
of any of the constituent materials. Specifically, particles form
bonds along the regions that have been forced into close contact
during pressing or compacting of these particles. Bonding occurs by
atoms moving into the vacancies between particle boundaries,
however, the particles are essentially the same size and shape
before and after the sintering process. Dimensional changes of the
compacted mixture are small. In addition, no liquid metal is
present at any stage during the solid state sintering process. To
further clarify, tungsten mobility is statistically insignificant,
if not absent, in the current invention due to the relatively low
processing temperature range.
[0033] During the solid state sintering process, neutral or
slightly reducing atmospheres may be used, since the oxide layer on
the outside of the powdered particles is mechanically smeared
during the pressing operation, which prepares the metal in these
regions for sinter bonding.
[0034] According to the current invention, a projectile 10 is
formed through a compaction and sintering process. As illustrated
in FIG. 1, the projectile 10 has a modified spherical shape after
the compaction and sintering processes have occurred. Further, what
is illustrated in FIG. 1 is a compacted and sintered mixture of a
plurality of tungsten particles and a plurality of iron particles,
which form the basic constituents of the projectile 10. At least
portions of the plurality of iron particles are bonded together.
Importantly, during the compacting and sintering processes, no
intermetallic compounds, alloys or metal matrices of the tungsten
particles and the iron particles are formed. In addition, the final
density of the projectile 10 is from about 8.1 grams per cubic
centimeter to about 12.1 grams per cubic centimeter and is nearly
the same before and after sintering. In addition, during the
sintering process, no substantial densification occurs.
[0035] The present invention uses tungsten particles and iron
particles that are much larger than those used in the prior art. In
one embodiment, the tungsten particles are from about 8 microns to
about 30 microns in diameter, and the iron particles are from about
40 microns to about 200 microns in size. Various forms of iron
particles may be utilized in the current invention. For example,
these iron particles may be water-atomized iron particles, reduced
iron particles, iron powder, etc. Further, such iron powder is of a
type that is typically used for pressed metal compositions. The use
of such iron powder allows for a higher pressed density than is
exhibited in the prior art, which uses fine, relatively
incompressible carbonyl iron powder.
[0036] In one preferred and non-limiting embodiment, the tungsten
particles and iron particles are formed into the projectile 10
through a compaction process. For example, the tungsten particles
and iron particles may be mechanically compacted in a die. Still
further, the tungsten particles and the iron particles may be
pre-blended prior to this compaction. After compaction, the
compacted or pressed density varies according to the composition of
tungsten and iron used. In one example, the pressed density is as
follows:
1 Density Percent Theoretical Tungsten:Iron Range (g/cm.sup.3)
Density 50:50 8.9-10.5 80-95% 55:45 9.3-11.0 80-95% 60:40 9.7-11.5
80-95% 65:35 10.2-12.1 80-95%
[0037] FIGS. 2 and 3 illustrate one embodiment of the
microstructure of the projectile 10 after the compaction process.
It should be noted that, as evidenced by the further micrograph
illustrations, the resulting projectile 10 has a high degree of
porosity and no interconnected tungsten particles.
[0038] During the forming process, such as in the compaction
process, various material additives may be used. For example, the
material additive may be a chemical compound, a polymeric compound,
a lubricant, a binder, etc. For example, polymeric additives may be
used and varied depending upon the forming process, but these
material additives may also include certain metals or metal
compounds to further effect and enhance the sintering process. In
addition, these additives may enhance the physical and/or chemical
characteristics and properties of the projectile after sintering.
Simple polymer additions for die compaction may be used to reduce
die wall friction.
[0039] In one embodiment, the chemical additive is a lubricant, and
the lubricant is added to a mixture of the tungsten particles and
iron particles during the compaction process. In one preferred and
non-limiting embodiment, the lubricant comprises up to 1% by weight
of the mixture. While the material additive may be any compound
suitable to enhance the physical and/or chemical characteristics of
the projectile 10 and the manufacturing process, in one embodiment,
the material additive may be ethylenebisstearimide (Acrawax C),
lithium carbonate compound, a stearate compound, a copper stearate,
a zinc stearate, etc.
[0040] After compaction, the projectile 10 is sintered, such as in
a sintering furnace, under controllable atmospheric conditions. The
temperature of the sintering process may be from about 1500.degree.
F. (815.degree. C.) to about 2450.degree. F. (1343.degree. C.). One
example of the operating range of the sintering process is
illustrated in FIG. 4.
[0041] The controllable atmospheric conditions may include the use
of a mildly oxidizing gaseous material, an inert gaseous material,
a reducing gaseous material, etc. In addition, as discussed above,
the projectile 10 is sintered in a solid state sintering process
relying on surface diffusion and grain boundary diffusion as the
predominate mechanisms for practical bonding, such that no liquid
metal or pore annihilation are present at any stage during the
process. In addition, no intermetallic materials, alloys or metal
matrices are formed during this solid state sintering process,
chiefly due to the sintering temperature discussed above and by the
use of particles with a mean size greater than, for example, 6
microns.
[0042] After compaction and sintering, the final density of the
projectile 10 is from about 8.1 grams per cubic centimeter to about
12.1 grams per cubic centimeter. Again, the final density ranges
according to the ratio of tungsten to iron used in projectile 10.
In one embodiment, the final density for various ratios of tungsten
and iron are as follows:
2 Density Percent Theoretical Tungsten:Iron Range (g/cm.sup.3)
Density 50:50 8.9-10.5 80-95% 55:45 9.3-11.0 80-95% 60:40 9.7-11.5
80-95% 65:35 10.2-12.1 80-95%
[0043] It should be noted that there is no appreciable
densification and the density after sintering is essentially the
same as it was prior to the sintering process, since the
densification of the projectile 10 is achieved during the
compaction process, which, as discussed above, uses mechanical bond
formation to form the projectile 10. FIG. 5 graphically illustrates
the relationship between sintered density, tungsten content and
percent of theoretical density.
[0044] The final hardness of the projectile 10 after sintering is
in the range of about 10 HRB to about 80 HRB. Also, the ratio of
tungsten particles to iron particles is variable, as discussed
above. For example, the mixture of tungsten particles to iron
particles may be, by weight, from about 30:70 to about 65:35.
[0045] The compacted and sintered projectile 10 may be a shot
pellet, a bullet, etc. In addition, the final hardness of the
formed and sintered projectile 10 is less than the final hardness
of steel shot. Still further, the resulting projectiles 10 are
essentially non-fragmenting and exhibit a high degree of
ductility.
EXAMPLE 1
[0046] In one preferred and non-limiting embodiment of the present
invention, the projectile was prepared by blending 45% Titan 24
micron tungsten powder (TW24), 54.7% A-1000-B iron powder (as
supplied by ARC Metals) and 0.3% Acrawax. Five hundred pounds of
this mixture was blended in a Patterson-Kelly Twin Shell "V"
blender for twenty minutes. The mixture had an apparent density of
4.4 grams per cubic centimeter and a flow of 19 s/50 g (Arnold
meter). Multiple lots were tested for apparent density and flow.
The results of this testing are as follows:
3 Lot Apparent density (g/cc) Flow (s/50 g) 1 4.49 18.5 2 4.48 19 3
4.46 19.5
[0047] Next, the mixture of tungsten and iron was pressed in a
high-speed rotary tablet press (Stokes BB2, 33-station) using
modified spherical tooling with a nominal die size of 0.187 inches.
The projectiles had a nominal density of 9 grams per cubic
centimeter, which was obtained by dividing the geometric volume in
cubic centimeters by the weight in grams. In order to reduce
individual measurement variations, groups of ten were collected and
measured. In addition, these volumetric measurements were compared
to certified density measurements made by Archimedes technique at a
certified, accredited testing laboratory. Results were early
identical to the volumetric-based measurements.
4 Percent Theoretical Sample Density (g/cc) Density 1 9.2 86% 2 9.1
85.5% 3 8.9 84%
[0048]
5 Percent Theoretical Sample Density (g/cc) Density 1 9.18 86% 2
9.03 85% 3 8.92 84%
[0049] The pressed projectiles were loaded into perforated steel
baskets (10.times.10.times.2 inches) at 10 pounds per basket and
fed into a 12-inch belt furnace with 2-inch gaps between the
baskets. The belt furnace used had a protective 90:10
nitrogen-hydrogen atmosphere flowing at a total of 500 SCFH.
Further, the furnace had two zones that were set for 1500.degree.
F. (pre-heat), and 2050.degree. F. (high-heat), and the belt speed
was set for 6 inches per minute.
[0050] The resulting sintered properties were measured at an
independent accredited certified testing laboratory. In particular,
the density was determined using the Archimedes technique (ASTM B
328), and the hardness was determined on the Rockwell HRB scale.
The results of these tests are as follows:
6 Density (g/cc) 9.15 (Average - 10 pcs) 86% of theoretic
mixture
[0051]
7 Sample Hardness (HRB) 1 33 2 32.1 3 22.1
EXAMPLE 2
[0052] In this example, the projectile 10 was prepared by blending
48% Titan 24 micron tungsten powder (TW24), 51.7% A-1000-B iron
powder (as supplied by ARC Metals), and 0.3% Acrawax. Ten pounds of
this mixture was blended by hand in a closed plastic container by
shaking and rolling the container for ten minutes.
[0053] Next, the mixture was pressed in a high-speed rotary table
press (Stokes BB1, 33-station) using modified spherical tooling
with a nominal die size of 0.187 inches. Pressed projectiles had a
nominal density of 9.3 grams per cubic centimeter. This nominal
density was determined as discussed above. In order to reduce
individual measurement variations, groups of ten were collected and
measured.
[0054] The compacted projectiles were loaded into a perforated
steel basket and fed into a 12-inch belt furnace, as discussed
above. In this example, the furnace had two zones that were set for
1500.degree. F. (pre-heat) and 2150.degree. F. (high-heat), and the
belt speed was set for six inches per minute.
[0055] The final density was determined using the Archimedes
technique (ASTM B 328), and the hardness of the projectile was
determined on Rockwell HRB scale. Again, these properties were
measured at an independent accredited certified testing laboratory.
The results of these texts are as follows:
8 Percent Theoretical Density (g/cc) Density 9.39 86% 9.3 85% 9.14
83%
[0056]
9 Sample Hardness (HRB) 1 29.4 2 36.3 3 37.5
EXAMPLE 3
[0057] In this example, the projectile was prepared by blending 52%
Titan 24 micron tungsten powder (TW24), 47.7% A-1000-B iron powder
(as supplied by ARC Metals), and 0.3% Acrawax. Ten pounds of this
mixture was blended by hand in a closed plastic container by
shaking and rolling the container for ten minutes.
[0058] The mixture was compacted in a high-speed rotary tablet
press as discussed above in connection with the previous examples.
The pressed projectiles had a nominal density of 9.8 grams per
cubic centimeter, as determined as discussed above. In order to
reduce individual measurement variations, groups of ten were
collected and measured.
[0059] Next, the pressed projectiles were loaded into a perforated
steel basket and fed into a 12-inch belt furnace used had a
protective 90:10 nitrogen-hydrogen atmosphere flowing at a total of
500 SCFH. The furnace had two zones that were set for 1500.degree.
F. (pre-heat) and 2125.degree. F. (high-heat), and the belt speed
was set for six inches per minute.
[0060] The density and hardness were measured by an accredited,
certified testing laboratory, as discussed above, using the
Archimedes technique and a hardness scale of Rockwell HRB. The
results of these tests are as follows:
10 Percent Theoretical Density (g/cc) Density 9.64 86% 9.68 86%
10.31 91%
[0061]
11 Sample Hardness (HRB) 1 15.4 2 14.6
[0062] The present invention provides a projectile 10 and method of
manufacturing this projectile 10, which results in a projectile 10
that has beneficial non-fragmenting and high ductility properties.
The sintered tungsten iron projectile 10 is softer than either of
the constituent materials due to the retained porosity, which
allows movement of the materials under load. Again, this porosity
is illustrated in FIGS. 2 and 3. Further, this porosity allows
deformation of the iron particles, which is essentially an open
web-like structure with tungsten particles locked within it. The
iron particles, which are bonded together after sintering, are soft
enough to deform under moderate load, and the sintering temperature
is high enough to promote sufficient iron-to-iron bonding, yet low
enough to avoid significant shrinkage due to sinter-densification
or the formation of brittle intermetallic compounds.
[0063] The tungsten particles are simply mechanically wedged
between the iron particles in a pressure-formed mechanical
impingement. The operating window for tungsten iron projectiles 10
according to the present invention is roughly defined by those
conditions that allow the material to remain soft by retaining
greater than approximately 5% porosity after sintering, while at
the same time reaching the desired density level by the appropriate
addition level of tungsten and pressed density. Further, the
present invention uses mechanical pressing to reach the final
density and sintering simply to enhance iron-to-iron bonding and
promote ductility. This invention has been described with reference
to the preferred embodiments.
[0064] Obvious modifications and alterations will occur to others
upon reading and understanding the preceding detailed description.
It is intended that the invention be construed as including all
such modifications and alterations.
* * * * *